1. Field of the Invention
The present invention relates to battery chargers and more particularly to an automatic polarity current control for charging rechargeable storage batteries.
This invention provides a storage battery polarity sensing circuit to be connected between a battery charger and the battery terminals without consideration of the polarity of the battery. This feature is desirable for the reason that regardless of the position of the battery cable clamps, when connected to the battery terminals, it is impossible to reverse charge the battery. This circuit also provides a safety feature in which no current is present at the battery terminal clamps until the battery cable clamps are connected with battery terminals. When battery charging terminal clamps are connected with a battery, as little as 2 volts potential from the battery positive terminal will energize this polarity circuit to match the polarity of the charging current with the polarity of the battery.
2. Description of the Prior Art
The most pertinent prior patents are believed to be U.S. Pat. Nos. 3,118,101; 3,406,318 and 3,413,487.
U.S. Pat. No. 3,118,101 discloses a bi-stable relay interposed in a circuit and normally energized and closed with primary contacts by rectified current from a transformer secondary winding for charging a storage battery in which residual battery current actuates the bi-stable relay to close with secondary contacts in the event the battery charging positive and negative cables are reverse polarity connected with the terminals of the battery.
The circuit of U.S. Pat. No. 3,406,318 features the inclusion of an impedance element in series with a field discharge diode to provide reverse polarity protection and prevent the destruction of a field switching transistor when a reverse polarity current is applied across the circuit.
The circuit of U.S. Pat. No. 3,413,487 features a pair of double-pole single throw relays connected in series with a respective diode across input terminals for storage battery potential closing of one or the other of the relays with its contacts and applying current to a storage battery in accordance with its polarity.
The circuit of this invention is distinctive over the circuits of the above named patents by utilizing the secondary winding of a transformer for charging a storage battery in accordance with the battery polarity which employs a plurality of silicon controlled rectifiers for rectifying the direction of current applied to the battery. The silicon controlled rectifiers are gated open in accordance with the polarity of residual potential of a connected storage battery by a like plurality of reed switches respectively connected with the gate of the respective silicon controlled rectifier.
This application is distinctive over the above referred to pending application by the inclusion of the manner in which the reed switches are connected with the respective end and center tap of the transformer secondary winding.